Does this strategy utilizing HELOC really work on saving money and paying off mortgages much quicker?  

Adding the current mortgage and utilities would be roughly $1,350 resulting in a profit of $650/mo.

I have also utilized owner financing for longer periods of time, including personal residence and 2 barrier island houses on the coast of Florida.  

This way you can utilize the leverage if you plan to scale up in the future.

Many Airbnb guests will want common utilities unless it is in a remote are where you go as a sot to sleep while hiking the area. 

Be sure to utilize tools of the trade for the best information.

And have you thought about building back utilities?

The tenants pay all utilities including sewer and garbage. 

If you’re looking at retrofitting to separate heating for each unit (like furnaces or mini-splits), you might be looking at a higher upfront cost, but it can shift utility expenses to tenants and improve your NOI.I’d factor in boiler age and efficiency when analyzing deals and if it’s near the end of its life, negotiate a price reduction or a credit.

@Kyle Trotman If you purchased with a hard money loan conventional lenders will require extensive seasoning to utilize the new appraised value for cash out.